Apparatus and method for making carbon nanotube array

ABSTRACT

An apparatus for making an array of carbon nanotubes includes a reaction chamber with a gas inlet and a gas outlet, a quartz boat disposed in the reaction chamber, a substrate with a surface deposited with a film of first catalyst, and a second catalyst disposed in the quartz beside the substrate. The substrate is disposed in the quartz boat.

RELATED APPLICATIONS

This application is a divisional application of patent application Ser.No. 11/371,997 filed on Mar. 8, 2006 from which it claims the benefit ofpriority under 35 U.S.C. 120. The patent application Ser. No. 11/371,997in turn claims the benefit of priority under 35 USC 119 from ChinesePatent Application 200510033733.6, filed on Mar. 8, 2005.

BACKGROUND

1. Technical Field

The disclosure relates generally to apparatuses and methods for makingcarbon nanotubes, and more particularly to an apparatus and a method formaking an array of carbon nanotubes.

2. Discussion of Related Art

Carbon nanotubes were discovered by S. Iijima in 1991, they are verysmall tube-shaped structures, each essentially having compositionsimilar to that of a graphite sheet rolled into a tube. Theoreticalstudies showed that carbon nanotubes exhibit either metallic orsemiconductive behavior depending on the radii and helicity of thetubules. Carbon nanotubes have interesting and potentially usefulelectrical and mechanical properties, and have many potential uses inelectronic devices. Carbon nanotubes also feature extremely highelectrical conductivity, very small diameters (much less than 100nanometers), large aspect ratios (i.e. length/diameter ratios greaterthan 1000), and a tip-surface area near the theoretical limit (thesmaller the tip-surface area, the more concentrated the electric field,and the greater the field enhancement factor). These features makecarbon nanotubes ideal candidates for electron field emitters, whitelight sources, lithium secondary batteries, hydrogen storage cells,transistors, and cathode ray tubes (CRTs).

Generally, there are three methods for manufacturing carbon nanotubes.The first method is the arc discharge method, which was first discoveredand reported in an article by Sumio Iijima entitled “HelicalMicrotubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp.56-58). The second method is the laser ablation method, which wasreported in an article by T. W. Ebbesen et al. entitled “Large-scaleSynthesis of Carbon Nanotubes” (Nature, Vol. 358, 1992, pp. 220). Thethird method is the chemical vapor deposition (CVD) method, which wasreported in an article by W. Z. Li entitled “Large-scale Synthesis ofAligned Carbon Nanotubes” (Science, Vol. 274, 1996, pp. 1701).

In the arc discharge method, a carbon vapour is created by an arcdischarge between two carbon electrodes either with or without acatalyst. Carbon nanotubes self-assemble from the resulting carbonvapour. In the laser ablation technique, high-powered laser pulsesimpinge on a volume of carbon-containing feedstock gas (methane orcarbon monoxide). Carbon nanotubes are thus condensed by the laserablation and are deposited on an outside collector. However, the carbonnanotubes produced by the arc discharge and the laser ablation varygreatly in diameter and length, with little control over the dimensionsof the resulting product. Moreover, poor carbon nanotube yield andprohibitive cost involved in making the device mean that the two methodsdifficult to scale up to suit industrial production.

In the chemical vapour deposition (CVD) method, carbon filaments andfibers are produced by thermal decomposition of a hydrocarbon gas on atransition metal catalyst in a chemical vapour deposition reactionchamber. In general, the chemical vapour deposition process results inboth multi-walled nanotubes (MWNTs) and single-walled nanotubes (SWNTs)being produced. Compared with the arc discharge method and laserablation method, the chemical vapour deposition method is a more simpleprocess and can easily be scaled up for industrial production. However,the carbon nanotubes manufactured by the chemical vapour depositionprocess aren't bundled to form an array, thus the CVD process can'tassure both quantity and quality of production.

In view of the above, another method, such as a thermal chemical vapordeposition method is disclosed where an array of carbon nanotubes areformed vertically aligned on a large-size substrate. The thermal CVDmethod includes the steps of: forming a metal catalyst layer on asubstrate; etching the metal catalyst layer to form isolated nano-sizedcatalytic metal particles; growing carbon nanotubes from said isolatednano-sized catalytic metal particles by the thermal chemical vapordeposition (CVD) process; and purifying the carbon nanotubes in-situ.

The carbon nanotubes formed by the above-described methods arevertically aligned on the substrate. However, the devices used inabove-described method are complicated. Several gas inlets are disposedin the device for introducing different gases. Also the carbon nanotubesformed by the above-described devices and methods are generallycomprised of a mix of MWNTs and SWNTs. The mixed carbon nanotubes do notsufficiently exhibit the useful properties of a single-type array ofcarbon nanotubes. Furthermore, excess amorphous carbon lumps and metalcatalyst lumps are also produced along with the carbon nanotubes formedby the above-described devices and methods and adhere to inner or outersidewalls of the carbon nanotubes. Thus, a complicated purificationdevice and method is required in addition to the above-described devicesmethods. Moreover, the devices used in the above-described methodgenerally operate at temperatures in the range from 700° C. to 1000° C.for growing carbon nanotubes, thus requiring a highly heat-resistantreaction chamber. Therefore, the devices in the above-described methodfor making the carbon nanotubes are limited.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments.

FIG. 1 is a schematic, cutaway view of an apparatus for making an arrayof carbon nanotubes in accordance with a first embodiment of the presentdisclosure;

FIG. 2 is a top view of a quartz boat with a substrate and a secondcatalyst thereon of FIG. 1;

FIG. 3 is a schematic, cutaway view of an apparatus for making an arrayof carbon nanotubes in accordance with a second embodiment of thepresent disclosure;

FIG. 4 is a cross-sectional, top view of a quartz boat of FIG. 3;

FIG. 5 is a side view of the quartz boat of FIG. 3;

FIG. 6 shows a Scanning Electron Microscope (SEM) image of the array ofcarbon nanotubes formed by the apparatus of FIG. 1; and

FIG. 7 shows a Transmission Electron Microscope (TEM) image of the arrayof carbon nanotubes formed by the apparatus of FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate at least one preferred embodiment of the disclosure, in oneform, and such exemplifications are not to be construed as limiting thescope of the disclosure in any manner.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe embodiments ofthe present apparatus and method for making an array of carbonnanotubes, in detail.

Referring to FIGS. 1 and 2, an apparatus 100 in accordance with a firstembodiment of the present device is provided. The apparatus 100 includesa reaction chamber 190, a quartz boat 150, a substrate 110, a firstcatalyst 130 and a second catalyst 170. The reaction chamber 190 can bea tubular container. A gas inlet 192 and a gas out let 194 are locatedat two opposite ends of the reaction chamber 190 respectively. In thepreferred embodiment, the gas inlet 192 is for introducing a carrier gasand a carbon source gas. The quartz boat 150 is disposed in the reactionchamber 190. The quartz boat 150 can be opened at two opposite ends. Inthe preferred embodiment, the quartz boat 150 is cymbiform.Alternatively, the quartz boat 150 could be made by other suitablematerials. The substrate 110 is disposed on the bottom of the quartzboat 150. The film of catalyst 130 is uniformly disposed on the surfaceof the substrate 110 by means of chemical vapor deposition, thermaldeposition, electron-beam deposition, or sputtering. The first catalyst130 can be made of iron (Fe), cobalt (Co), nickel (Ni), or anycombination alloy thereof. In the preferred embodiment, the firstcatalyst 130 is made of iron. The second catalyst 170 is disposedproximate to the substrate 110. The second catalyst 170 and thesubstrate 110 are disposed on the bottom of the quartz boat 150. Thesecond catalyst 170 is placed beside one side of the substrate 110. Thesecond catalyst 170 can be either metallic powder or netting made ofiron, nickel or alumina. In the preferred embodiment, the secondcatalyst 170 is iron powder. In the first embodiment, a first route isdefined in the reaction chamber 190 for the introduced carbon source gasflow from the second catalyst 170 toward the substrate 110. The secondcatalyst 170 is disposed on the route. The second catalyst 170 canpyrolize the introduced carbon source gas to produce a small amount ofhydrogen gas which then flows toward the substrate 110. In the preferredembodiment, the second catalyst 170 is disposed proximate to one side ofthe substrate 110 facing the gas inlet 192. The additional hydrogenactivates the first catalyst 130 and reduces the concentration of carbonsource gas around the first catalyst 130. Therefore, the growth speed ofthe carbon nanotubes is increased and the height of the array of thecarbon nanotubes is enhanced. In addition, advantageously, the hydrogenproduced by the second catalyst 170 and the carbon source gas can reachthe first catalyst 130 along the route and activate the first catalyst130 to improve the growing speed of the carbon nanotubes.

Referring to FIGS. 3, 4 and 5, an apparatus 200 in accordance with asecond embodiment of the present device is provided. The apparatus 200includes a reaction chamber 290, a quartz boat 250, a substrate 210, afirst catalyst 230 and a second catalyst 270. The reaction chamber 290can be a tubular container. A gas inlet 292 and a gas out let 294 arelocated at two ends of the reaction chamber 290 respectively. In thepreferred embodiment, the gas inlet 292 is for introducing a carrier gasand a carbon source gas. The quartz boat 250 is disposed in the reactionchamber 290. The quartz boat 250 includes an open end. In the preferredembodiment, the quartz boat 250 is tubular with one open end facingtowards the gas inlet 292. The substrate 210 is disposed in the quartzboat 250. The film of first catalyst 230 is uniformly disposed on thesurface of the substrate 210 by means of chemical vapor deposition,thermal deposition, electron-beam deposition, or sputtering. The firstcatalyst 130 can be made of iron (Fe), cobalt (Co), nickel (Ni), or anycombination alloy thereof. In the preferred embodiment, the firstcatalyst 230 is made of iron. The second catalyst 270 is disposedproximate to the substrate 110. The quartz boat 250 includes a bottomand at least one sidewall extending from the bottom, the second catalyst270 is disposed on the bottom and between the substrate 210 and the atleast one sidewall of the quartz boat 250. The second catalyst 270 andthe substrate 210 are disposed on the bottom of the quartz boat 250. Thesecond catalyst 270 can be either metallic powder or metal netting madeof iron, nickel or alumina. In the preferred embodiment, the secondcatalyst 270 is iron powder. In the second embodiment, a second route isdefined in the quartz boat 250 for the introduced carbon source gas flowfrom the second catalyst 270 toward the substrate 210. The secondcatalyst 270 is disposed beside three sides of the substrate 210 farfrom the gas inlet 292. The second catalyst 270 pyrolizes the carbonsource gas to produce small quantities of hydrogen gas which flowstowards the first catalyst 230. The additional hydrogen activates thefirst catalyst 230 and reduces the concentration of carbon source gasaround the first catalyst 230. Therefore, the growth speed of the carbonnanotubes is increased and the height of the array of the carbonnanotubes is improved. In addition, advantageously, the hydrogenproduced by the second catalyst 270 and the carbon source gas can reachthe first catalyst 230 along the second route and activate the firstcatalyst 230 to improve the growing speed of the carbon nanotubes.

A preferred method for making an array of carbon nanotubes using thepresent apparatus is provided. In the preferred embodiment, the methodis based on the first embodiment and includes the following steps in noparticularly order thereof. Firstly, a substrate 110 with a surface isprovided, and a film of first catalyst 130 is formed on a surface of thesubstrate 110. The film of first catalyst 130 is uniformly disposed onthe substrate 110 by means of chemical vapor deposition, thermaldeposition, electron-beam deposition, or sputtering.

Secondly, a quartz boat 150 and a second catalyst 170 are provided. Thesecond catalyst 170 and the substrate 110 are disposed on a bottom ofthe quartz boat 150. The second catalyst 170 is disposed proximate tothe substrate 110.

Thirdly, a horizontal reaction chamber 190 with a gas inlet 192 and agas outlet 194 is provided. The gas inlet 192 is for introducing acarrier gas and a carbon source gas. The quartz boat 150 is disposed ona bottom of the reaction chamber 190. A first route is defined in thereaction chamber 190 for the introduced carbon source gas flow from thesecond catalyst 170 to the substrate 110. The second catalyst 170 andthe substrate 110 are disposed on the route. In the preferredembodiment, the second catalyst 170 is disposed proximate to at leastone side of the substrate 110 far from the gas outlet 194.

Fourthly, a carrier gas is continuously introduced into the reactionchamber 190 from the gas inlet 192 at one atmosphere of pressure. Thecarrier gas is used to create an atmosphere of inert gas in the reactionchamber 190. Then, the reaction chamber 190 is heated gradually to apredetermined temperature. A carbon source gas which mixes with thecarrier gas is introduced into the reaction chamber 190 from the gasinlet 192. The carrier gas can be a nitrogen (N₂) gas or a noble gas.The carbon source gas can be ethylene (C₂H₄), methane (CH₄), acetylene(C₂H₂), ethane (C₂H₆) or any combination thereof. In the preferredembodiment, the carrier gas is argon (Ar), the carbon source gas isacetylene. A ratio of the carrier gas flow-rate to the carbon source gasflow-rate can be adjusted in the range from 5:1 to 10:1. In thepreferred embodiment, the argon flow-rate is 300 sccm (Standard CubicCentimeter per Minute), and the acetylene flow-rate is 30 sccm. Thepredetermined temperature used in the method can be in the range from600 to 720° C. In the preferred embodiment, the predeterminedtemperature is in the range from 620 to 690° C.

Due to catalyzing by the first catalyst 130, the carbon source gassupplied into the reaction chamber 190 is pyrolized in a gas phase intocarbon units (C═C or C) and free hydrogen (H₂). The carbon units areabsorbed on a free surface of the first catalyst 130 and diffused intothe first catalyst 130. When the first catalyst 130 is supersaturatedwith the dissolved carbon units, carbon nanotube growth is initiated. Asthe intrusion of the carbon units into the first catalyst 130 continues,an array of carbon nanotubes is formed. The array of the carbonnanotubes formed by the preferred embodiment is a multi-walled carbonnanotube array. Density, diameter and length of the multi-walled carbonnanotube array can be controlled by adjusting the flow rates of thecarbon source gas and the carrier gas, and by altering the predeterminedtemperature and the reaction time. In addition, the second catalyst 170used in the first embodiment can act on the carbon source gas. Thesecond catalyst 170 can pyrolize the carbon source gas to produce asmall amounts of hydrogen gas which flows to the first catalyst 130. Theadditional hydrogen produced by the second catalyst 170 can activate thefirst catalyst 130, and further reduce the concentration of the carbonsource gas around the first catalyst 30. As such, the growth speed ofthe carbon nanotubes is increased and the height of the array of thecarbon nanotubes is enhanced. In the preferred first embodiment, thereaction time is in the range from 30 to 60 minutes. The synthesismethod can produce carbon nanotubes with a length greater than 3-400micrometers, and have a diameter in the range from 10 to 30 nanometers.

Referring to FIGS. 6 and 7, an SEM image and a TEM image of themulti-walled carbon nanotube array formed by the present device areshown. It can be seen that the-carbon nanotubes in the array of thecarbon nanotubes are highly bundled and super-aligned. The height of thearray of the carbon nanotubes is about 300 micrometers.

In the present apparatus and method, the second catalyst 170, 270 can bemetallic powder or netting made of pure iron or nickel. During thesynthesis process of the array of the carbon nanotubes, the secondcatalyst 170, 270 pyrolizes the carbon source gas to produce smallamounts of hydrogen. The hydrogen can activate the first catalyst 130,230 and reduce the consistency of the carbon source gas around the firstcatalyst 130, 230. As such, the growth speed of the carbon nanotubes isimproved and the height of the array of the carbon nanotubes can be froma few hundred micrometers to a few millimeters.

In the preferred methods, the method for making the second catalyst 170,270 powder includes the following steps in no particular order thereofFirstly, a powder of about 11.32 grams of ferric nitrate and about 8 gof alumina are immersed in an ethanol solution of 100 milliliters.Secondly, the mixture solution is stirred for about eight hours, andthen vaporized by a revolving evaporator for about 12 hours at atemperature of about 80° C. Thirdly, the remainder after vaporizing isball milled to produce a second catalyst powder. In addition, the secondcatalyst 170, 270 powder used in the present apparatus and method can berecycled. After the synthesis process of the array of the carbonnanotubes, the second catalyst 170, 270 powder can be collected from thequartz boat 150, 250. Then, the collected powder can be burned in anoxygen atmosphere to remove the carbon nanotubes and amorphous carbonwhich adhere to the second catalyst 170, 270. As such, the secondcatalyst 170, 270 powder can be used many times and thus the use of thesecond catalyst adds almost no additional cost.

Furthermore, it is noted that, the shape of the quartz boat of thepresent apparatus can be varied. The disposed place of the secondcatalyst relates to the shape of the quartz boat and the direction ofthe gas flowing in the quartz boat. In particularly, when the quartzboat is cymbiform including two opposite open ends with one end facingtowards the gas inlet and the other facing towards the gas outlet of thereaction chamber (referring to the first embodiment of the presentapparatus), the second catalyst is disposed beside at least one side ofthe substrate far from the gas outlet. Alternatively, when the quartzboat is tubular including one open end facing to the gas inlet(referring to the second embodiment of the present apparatus), thesecond catalyst is disposed beside at least one side of the substratefar from the gas inlet. Furthermore, because the purpose of adopting thesecond catalyst in accordance with the present apparatus and method isproviding small amounts of additional hydrogen gas around the film offirst catalyst, the disposing of the second catalyst should obey thefollowing conditions. Firstly, that the second catalyst should bedisposed beside the substrate to assure that the produced hydrogen bythe second catalyst can act on the first catalyst directly. Secondly,that the second catalyst should be disposed in front of the substratealong a direction of gas flow that ensures that the hydrogen produced bythe second catalyst can reach the first catalyst. Also, it is to beunderstood that the second catalyst should be placed within the range ofprotection of the present apparatus and methods.

It is noted that, the reaction chamber of the present apparatus includesapparatuses for use in chemical vapor deposition, such as horizontal CVDdevices, vertical CVD devices and a CVD device with a removable quartzboat. Moreover, the present apparatus and method can synthesize massivecarbon nanotube arrays by disposing a plurality of substrate in thereaction chamber simultaneously, and that the property of carbonnanotubes thus produced is essentially uniform. Thus, both quality andproduction of the carbon nanotubes can be controlled by the presentapparatus and method. Furthermore, the film of first catalyst of thepresent apparatus and method can be patterned for growing patternedcarbon nanotube array.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the disclosure. Variations maybe made to the embodiments without departing from the spirit of thedisclosure as claimed. The above-described embodiments illustrate thescope of the disclosure but do not restrict the scope of the disclosure.

1. An apparatus for making an array of carbon nanotubes, comprising: areaction chamber having a gas inlet introducing a carbon source gas anda carrier gas thereinto and a gas outlet; a substrate having a layer offirst catalyst provided thereon, the substrate being disposed in thereaction chamber; and a second catalyst reacting with the carbon sourcegas thereby producing a resultant product promoting catalytic activityof the first catalyst, wherein the reaction chamber defines a firstcarbon source gas route towards the substrate; the second catalyst isdisposed on the route.
 2. The apparatus as claimed in claim 1, furthercomprising a boat supporting the substrate.
 3. The apparatus as claimedin claim 2, wherein the boat is a quartz boat.
 4. The apparatus asclaimed in claim 2, wherein the second catalyst is disposed proximate tothe substrate.
 5. The apparatus as claimed in claim 1, wherein thesecond catalyst is comprised of iron, nickel, and alumina.
 6. Theapparatus as claimed in claim 1, wherein the first catalyst is comprisedof iron, cobalt, nickel, and any combination alloy thereof
 7. Theapparatus as claimed in claim 1, wherein the reaction chamber issubstantially tubular-shaped.
 8. An apparatus for making an array ofcarbon nanotubes, comprising: a reaction chamber having a gas inletintroducing a carbon source gas and a carrier gas thereinto and a gasoutlet; a substrate having a layer of first catalyst provided thereon,the substrate being disposed in the reaction chamber; a second catalystreacting with the carbon source gas thereby producing a resultantproduct promoting catalytic activity of the first catalyst; and atubular boat receiving the substrate and the second catalyst therein,the tubular boat having an open end introducing the carbon source gasthereinto and an opposite closed end blocking and directing theintroduced carbon source gas in the boat to flow toward the substrate,wherein the second catalyst is disposed in the boat in a manner toenable the resultant product associated with the second catalyst toforcedly flow toward the substrate.
 9. The apparatus as claimed in claim8, wherein the boat includes a bottom and at least one sidewallextending from the bottom; the second catalyst is disposed on the bottomand between the substrate and the at least one sidewall of the boat. 10.An apparatus for making an array of carbon nanotubes, comprising: areaction chamber having a gas inlet and a gas outlet; a hollow containerdisposed in the reaction chamber and having only one opening oriented tothe gas inlet; a substrate contained in the hollow container, thesubstrate having a top surface, a bottom surface contacting the hollowcontainer, and a side surface extending from the top surface to thebottom surface; a first catalyst disposed on the top surface; a secondcatalyst contained in the hollow container and distributed along theside surface of the substrate except at parts of the side surface facingthe gas inlet.
 11. The apparatus as claimed in claim 10, wherein thehollow container comprises a sidewall and a peripheral wall extendingfrom a periphery of the sidewall towards the gas inlet.
 12. Theapparatus as claimed in claim 11, wherein both the bottom surface andthe second catalyst directly contact the peripheral wall of the hollowcontainer.
 13. The apparatus as claimed in claim 12, wherein the secondcatalyst contacts the side surface except at the parts of the sidesurface facing the gas inlet.
 14. The apparatus as claimed in claim 13,wherein the first catalyst is comprised of iron, cobalt, nickel, and anycombination alloy thereof.
 15. The apparatus as claimed in claim 13,wherein the second catalyst is metallic powder or netting made of pureiron or nickel.
 16. The apparatus as claimed in claim 11, wherein theperipheral wall perpendicularly extends from the periphery of thesidewall and defines the only one opening.